This invention relates in general to prosthetic devices, and more particularly to articulated prosthetic ankle joints.
Each foot and ankle during walking travel through stance and swing phases of a gate cycle. In the stance phase, the foot is in contact with the ground and the weight of a person is supported on the foot. In the swing phase, the foot is off the ground as the entire leg and foot move from a posterior position to an anterior position with respect to a center of gravity of the person. The stance phase begins just after completion of the swing phase and commences with a heel strike wherein the foot is lowered to the ground as the body moves forward from a position posterior to the person""s center of gravity. Immediately after heel strike, the foot moves from a dorsiflexed position, wherein the toes of the foot are pointed upwards, to a plantarflexed position wherein the bottom of the foot or shoe is flat on the walking surface, which provides greater stability as the entire weight of the person is shifted over the foot in contact with the ground. The swing phase commences just after heel strike of the other foot. During the swing phase, the foot is again in the dorsiflexed position as the foot leaves the walking surface and the foot and leg swing forward in preparation for the stance phase. Dorsiflexion is essential for normal human locomotion, since the toes must be dorsiflexed in order to clear the floor. If the foot were not dorsiflexed during the swing phase, it would most likely catch on the walking surface and cause the person to stumble and fall, leading to potentially serious injury.
For the purposes of this disclosure, the term medial refers to the person""s center of gravity, whereas the medial movement is the sidewise, inward movement toward the center of gravity. The term lateral motion is defined herein as the sidewise outward movement from the center of gravity. In the neutral or medial position the interior and exterior parts of the foot are positioned substantially horizontally. Two inclined positions of the human foot in both directions from the vertical are defined herein as inversion and eversion. The inversion or inverted position occurs when an exterior part of the foot is sloped downwardly, while an interior part of the foot is directed upwardly. In the opposite respect, the eversion or inverted position of the foot occurs when the exterior part of the foot is directed upwardly and the interior part of the foot slopes downwardly. The inclination of the human foot in the inverted and everted positions ranges between 0xc2x0 and 15xc2x0 to the horizontal plane.
There are currently available prosthetic ankle joints which are designed to assist a user during walking or travel through stance and swing phases of a gait cycle. An example of such modern prosthetic ankle joint is provided by U.S. Pat. No. 6,187,052 which is incorporated by reference by the present application. However, the movements of the human foot are so complex, so that even this sophisticated prosthetic device does not imitate some important aspects of the human ankle movement during walking. In this respect, the available prior art prosthetic ankle joints are not fully capable of movement from side to side, so as to encompass the required range of movements of the human ankle in the above-discussed inversion and eversion positions accompanied by the controlled return thereof to the medial or neutral position. Therefore, the known prior art prosthetic devices cannot efficiently accommodate a combination of slopes in sideward fashion that act upon the bottom of the foot during travel by an amputee.
Thus, it has been long felt and unsolved need for a prosthetic ankle unit which is capable of imitating important aspects of the human ankle movements during walking including inclined positions such as the inversion and eversion movements, so as to enable the prosthetic foot to accommodate slopes and other types of uneven terrain. In the present invention this is accomplished by positioning of a base member between resilient biasing members, so as to provide a multi-axial, self-centered prosthetic ankle joint, which, after achieving such inclined positions, tends to return the base member and the prosthetic foot connected thereto to the medial or neutral state.
One aspect of the invention provides a prosthetic ankle joint for connection between a pylon and a prosthetic foot. The prosthetic ankle joint includes a base member which consists of an upper base portion and a lower base portion. The lower base portion is formed with a substantially hollow receiving inner cavity extending inwardly from an end thereof remote from the upper base portion. The base member is movably positioned within the receiving inner cavity and is connected to a prosthetic foot. The base member is movable in the side-to-side direction relative to the base, so as to enable the prosthetic foot to closely follow a walking surface.
As to another aspect of the invention, the base member has an inverse T-shaped configuration and is arcuately movable within the receiving inner cavity. The base member comprises of an upright portion which extends outwardly from a lower portion in such a manner that first and second lower engaging portions are formed on either side of the upright portion. The first upper engaging portion and the first lower engaging portion define a first engaging zone and the second upper engaging portion and the second lower engaging portion define a second engaging zone.
As to a further aspect of the invention, a pair of resilient biasing members are freely positioned within the inner cavity, so as to face the respective first and second engaging zones of the base member. The first upper engaging portion is preferably substantially normal to the first lower engaging portion and the second upper engaging portion is preferably substantially normal to the second lower engaging portion.
Still another aspect of the invention provides the prosthetic ankle joint wherein coaxial apertures are formed within the anterior and posterior walls of the lower base portion. The upright portion of the base member contains an opening passing therethrough. The base member is movably supported within the lower base portion by a shaft passing through the aperture in the anterior and posterior walls and the opening in the upright portion.
A Still further aspect of the invention provides the prosthetic ankle joint, wherein an enclosed area is defined within the inner receiving cavity in one direction by the pair of biasing members facing the engaging zones; and in the other direction the enclosed area is defined by the inner surface of the anterior and posterior walls positioned in the vicinity of substantially flat anterior and posterior surfaces of the base member. During the arcuate motion of the base member a distance between the respective engaging zone of the base member and the inner cavity is decreased causing deformation of the respective biasing member interposed therebetween. The deformed biasing member forces the base member to return to a neutral position in which a vertical axis of the base member substantially coincides with the vertical axis of the base.
As to a still further aspect of the invention, a prosthetic ankle joint is provided which includes a base consisting of an upper base portion and a lower base portion. The lower base portion is formed with a substantially hollow receiving inner cavity extending inwardly from an end thereof remote from the upper base portion. A base member is movably positioned within the receiving cavity and is connected to a prosthetic foot. The base member has an inverse T-shaped configuration and comprises an upright portion which extends outwardly from the lower portion in such a manner that first and second engaging zones are formed on either side of the base member. A pair of resilient biasing members is provided within the receiving inner cavity, so as to face the respective first and second engaging zones and is adapted to limit and control the arcuate motion of the base member.